Texas A&M University designed, built, and tested a sodium boiler for Los Alamos National Laboratory. The boiler is a candidate subsystem for a 3 kWe Mars surface power reactor. A sodium boiler has been proposed to enhance transfer of thermal energy between the heat pipe cooled reactor core and the Stirling engine heater head. The heat transfer mechanism, and its efficiency, is important to the overall efficiency of the reactor power system. Uncertainty regarding the performance of the sodium heat exchanger, specifically boiling and condensing behavior, particularly in Martian gravity, led LANL to ask the Center for Space Power (CSP) at Texas A&M University to measure the effectiveness of such a device. Data included liquid and vapor sodium temperatures within the boiler, wall temperatures, and calorimetry data. Visualization of the sodium was provided by two quartz windows that allowed experimenters to see the sodium surface and the condensing head section. The boiler was tested to 1540 watts input power and 550 °C sodium pool temperature before braze failures caused experiment termination.